This is soemthing I've been experimenting with over the last 10 months since my own T1 diagnosis.
Generally I've bought it down to long ride/run rules and short ride/run rules.
Short rides or runs - less than one hour
If <2hours post meal, reduce your meal time bolus, depending on intensity you expect. Anywhere between 20% and 50%
Test pre, after half an hour and at the end.
Take quick acting and slow acting carbs with you, I tend to use gels or mini packets of haribos for quikc acting as they don't go icky in the pockets. Slower acting I have a variety of nut and fruit based bars, good high density energy, medium GI. Malt loaf is good as well.
If I'm doing something like long intervals or a tempo workout with a higher aerobic demand I'll test more often, say at the end of a 2km interval at race pace.
Longer runs/rides - Runs>90 mins, rides>2hr, these tend to be in the morning
1) reduce morning basal, Levemir in my case to 1 unit (normal 3.5)
2) reduce morning bolus to 1 unit, just to keep the carbs moving in the right direction. You may need to experiment with this, but I becoem extremely insulin sensitive
3) estimate your carb needs - I work on 60g per hour for steady distance work, varies depending on effort (wind, speed when cycling, pace and terrain when running), add on a safety margin and double my usual just in case emergency QA carbs. Long runs are done with a small pack/camelback.
4) test pre run/ride - this will be high. Test frequently, in my case 45 mins while cycling, 5km while running, you may want to be more frequent until you've understood your bodies response. In my case, as an example, I've started a run at 13.6 and 5km later been at 3.8. My target is to be steadily measuring at >5.5, <7.5
As for the mechanics of testing, for cycling, I just pull over to the side of the road, somewhere safe and do it there, for running I've developed it to the point where I slow to a walk to get everything ready, including pricking the finger, then the only thing I stop for is applying the blood to the sensor.
Hope that helps,
Dave